1. Technical Field of the Invention
The present invention relates to an X-ray CT apparatus and x-ray radiographic method that is adapted for switchover between a CT mode to obtain a tomographic image of a subject and a transmission mode to obtain a transmission image of the subject, depending upon the data acquired in the imager system thereof.
2. Description of the Related Art
The known X-ray CT (computerized tomography) apparatus, called the third generation, is oppositely arranged with an X-ray tube and an X-ray detector having a plurality of arrays of multi-channel X-ray detector elements, sandwiching a patient (subject). While rotating those through 360 degrees about the subject, an X-ray beam is irradiated from the X-ray tube to a predetermined region of the patient. The X-rays transmitted the predetermined region is measured as projection data by the X-ray detector. Based on the data, image reconstruction process is made by the use of a computer to thereby obtain a tomographic image as to the predetermined region.
In this manner, the X-ray CT apparatus usually provides nothing more than a tomographic image. However, during operation for example, there is a possible need of a transmission image on a region concerned of a subject, in addition to a tomographic image. This however requires an X-ray CT apparatus, serving also in a transmission mode, set up in an operating room.
However, the CT radiography with the existing X-ray CT apparatus tends to use an X-ray higher in intensity than that of the X-ray apparatus. The patient undergoes much exposure to X-ray radiation, thus being imposed with great burden.
Meanwhile, the X-ray apparatus having an I.I (image intensifier) requires a fine positional adjustment while actually irradiating X-rays to the patient after roughly positioning the patient relative to the apparatus. This places the patient under much exposure to X-ray radiation and hence imposes a great burden on the patient.